The art of transmitting information in an effective and reliable manner has been developed over a long period of time, and the introduction of electronic devices has resulted in increases in the rate at which information is transmitted as well as the reliability with which the information is transmitted.
To insure the reliability of the information transmitted, error detecting and correcting techniques have long been applied to the transmission of information. One conventional error detecting technique is to require the receiver of information to send a copy of the received information back to the transmitter. The transmitter can then compare the transmitted information with the received information, and assuming they are identical, assume that the receiver properly received the transmitted information. In the event that the transmitter notes a difference between the transmitted and received information, the transmitter is arranged to assume that the receiver improperly received the information, and the transmitter may retransmit the information.
Typically, in any information communication system, the transmitter and receiver are spaced apart and therefore must be coupled by some communication link or channel. In those applications in which the communication channel includes conductors, it has been apparent for some time that rather than employing dedicated conductors for each transmitter/receiver pair, it may be effective, if many transmitters are mostly idle, to add an additional unit for concentrating information derived from a plurality of transmitters so that the information is then transmitted from the concentrator on a single communication channel. This has proven to be an effective technique if the transmitters are usually idle and therefore, there is sufficient time between transmissions from one transmitter for transmitting information for others of the transmitters. The same concentration technique can be used when the communication channel is a frequency or time divided link.
Notwithstanding the foregoing conventional techniques, it has also been apparent for some time that the use of these techniques carriers with it certain disadvantages. When a concentrator is employed, the very presence of the concentrator requires apparatus in addition to that which would have otherwise been necessary had the concentrator not been added. Therefore, efforts have been made to simplify concentrators, and one of the objects of the present invention is to provide effective information transmission systems with a relatively simple concentrator and without loss of error detection and correction function.
The advent of the microprocessor, with its ability to perform varied functions, has meant that more and more intelligence can be distributed throughout an information communication system without paying a penalty of high costs. However, the simplification goal in such a system is not achieved by the mere presence of such a microprocessor. With the use of microprocessors, the penalty paid for undue complexity is now no longer hardware costs, but rather the cost of preparing suitable programs for each of the microprocessors in the system as well as the time taken by the processors in executing the instructions which might not have been necessary.